The purpose of this study is to determine net acid balance in infants and children with uremic acidosis or with the proximal or distal forms of renal tubular acidosis (RTA). The hypothesis to be tested is that children with uremic acidosis or distal RTA are in positive net acid balance as opposed to children with proximal renal tubular acidosis who are in zero net acid balance. This difference may explain the absence of bone disease in proximal RTA and the presence of nephrocalcinosis and hypercalciuria in distal RTA and bone disease in uremic acidosis through recruitment of bone salts as buffers with resultant dissolution of bone and release of calcium. During the first 8 months of this grant period, net balance has been determined in 2 children with chronic renal failure. In 1 of these children, a 3 month old infant, the overall net acid balance during correction of acidosis was stikingly negative. Thus, the amount of base retained during correction was distributed in a volume far in excess of total body water, implying that a large fraction of the net base entered non ECF buffers (probably skeletal). This confirms the previous studies demonstrating the importance of skeletal buffers in uremic acidosis. A similar study was performed on an infant with proximal RTA during correction of acidosis. Over a 96 hour period the negative hydrogen ion balance reflected the excretion of hydrogen ion necessary to effect the correction of acidosis. However, again the quantity of retained base was in excess of that required to achieve this degree of correction in total body water. These data can be interpreted as indicating that children with proximal RTA are in positive hydrogen ion balance and that bone does participate in the buffering of these hydrogen ions. If this is confirmed it would be contrary to our original hypothesis.